The primary goal of this project is an analysis of the genetic and biological role of DNA topoisomerase ll from Drosophila in the folding and segregation of eukaryotic chromosomes. The specific goals are to select both cDNA and genomic DNA fragments of the gene encoding the Drosophila DNA topoisomerase ll from libraries in expression vectors. Second, we wish to prepare expression vectors that could contain a complete copy of the cDNA for overproduction in bacteria and yeast. Third, we will locate the DNA topoisomerase gene in the genome by in situ hybridization and then prepare specific mutations in the enzyme. We will use the clones cDNA to complement these mutants and also attempt to complement existing lethal mutants in yeast DNA topoisomerase ll. We will also introduce copies of the gene back into Drosophila by the P-element mediated transformation system. These additional copies will be under regulated promoters so that the effect of additional DNA topoisomerase activity on chromosome structure can be observed. Mutants and anti-sense copies of the gene will be contructed in vitro and introduced into Drosophila to examine their biological effects. Finally we will use the cloned segments to locate the position of the normal gene along the polytene chromosomes in attempts to correlate its position with known mutants affecting chromosome metabolism.